use strict in JavaScript- What is it and how to use it?

use strict in JavaScript- What is it and how to use it?

Hey readers, in this article we will be discussing how to use the use strict method in JavaScript in a step-wise, efficient manner. If you are a beginner and want to learn JavaScript then do check out the course on Codedamn.


JavaScript is one of the most used languages when it comes to building web applications as it allows developers to wrap HTML and CSS code in it to make web apps interactive. It allows a web application to be interactive. It is also used for making animations on websites and has a large community on GitHub. JavaScript has tons of libraries, one of which is React which we will be covering in this article later. 

Use cases: 

  • Building web server and its interactive functions
  • Animations and graphics, adding special effects to web components
  • Validating forms and exception errors
  • Adding behavior and functionalities to web pages

Since JavaScript is a scripting language, it works without any libraries. Developers are free to write JavaScript language code anywhere and can still run it in the browser. There is no structure in JavaScript, the browser executes each line of the code from top to down.

use strict method

Strict Mode is a new feature in ECMAScript 5 that lets you put a program or function in a “strict” operating context. This stringent context makes it impossible to conduct certain actions and creates extra exceptions. The sentence “use strict” tells the browser to utilize the Strict version of JavaScript, which has a smaller and safer feature set.

Benefits of using ‘use strict’: Strict mode modifies the regular JavaScript semantics in various ways.

Strict mode converts some JavaScript silent mistakes to throw errors, which eliminates them.

Strict mode corrects errors that make optimizations difficult for JavaScript engines: Code written in strict mode can sometimes be made to execute quicker than code written in a non-strict manner.

Strict mode forbids some syntax that is anticipated to be defined in future ECMAScript versions.

When comparably “unsafe” actions are taken, it prevents or throws errors (such as gaining access to the global object).

It turns off features that are unclear or poorly designed.

Strict mode facilitates the creation of “secure” JavaScript.

Strict mode can be utilized in two ways. Keep in mind that block statements surrounded in braces will not work in strict mode.

For the entire script, it is used in the global scope.

It can be used for specific functions.

For the full script, use Strict mode: Put the exact statement “use strict”; (or ‘use strict’;) before any other statements to force strict mode for the whole script.

//  strict mode syntax

‘use strict’;

 let a = “strict mode script!”;

It is not possible to concatenate non-conflicting scripts using this syntax because it has a flow. Combining a strict mode script with a non-strict mode script is a good idea. The entire concatenation appears to be strict; yet, the opposite is also true. The non-strict plus strict combination appears to be non-strict. It’s fine to concatenate strict mode scripts with each other, and it’s also fine to concatenate non-strict mode scripts. It’s only a problem when strict and non-strict scripts are combined. As a result, it’s best if you enable strict mode function by function (at least during the transition period).

Using Strict mode for a function: To use strict mode for a function, place the exact statement “use strict”; (or ‘use strict’;) before any other statements in the function’s body.

Strict mode can be used in the following ways:

In standard JavaScript, mistyping a variable name result in the creation of a new global variable. This will generate an error in strict mode, making it impossible to create a global variable by accident.

// Using a variable, without declaring it, is not allowed:

‘use strict;

x = 3.14; // will throw an error

If you select strict mode, you won’t be able to utilize a variable that hasn’t been declared.

It is not possible to delete a variable (or object) or a function.

It is not permitted to use the same parameter name twice.

The use of octal numeric literals is prohibited.

There are no escape characters permitted.

It is not possible to write to a read-only property.

It is not possible to write to a get-only property.

It is not possible to delete an undeletable property.

It is not possible to use the string “eval” as a variable.

It is not possible to use the string “arguments” as a variable.

The use of the with statement is not permitted.

This value was the global object in function calls like f(). It is now undefined in strict mode. When giving values to non-writable attributes in standard JavaScript, the developer will not receive any error message.


This was about the use the strict method in JavaSript using HTML, if you want to learn more about javascript, do check out the article and course on Codedamn of javascript along with the course. Hope you liked this, if you have any queries or suggestions do let us know in the comments. 

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